I thought that I should share my experience in setting up my DW2 wifi L door contact.
It seemed to easily pair to my wifi extender but after a few minutes it went offline. It was positioned around 10 meters from the extender and had a strong signal.
I then paired to another access point and it stayed connected. Some searches online and I saw mention that the device does not work with an extender but needs an AP. I reconfigured my extender to an access point and all working now. Needed to run another lan cable of course.